


Laundry Day

by Gilded_Pleasure



Category: Undertale (Video Game)
Genre: At Least One(1) Cock Probably, Everyone is Trans, I have no possible way to prepare you for this you’ll just have to go with it, It’s got a good beat and you can fap to it, Kissing, Multi, Other, Penetrative Sex, Porn With Plot, Porn with Feelings, Several Recognizable Sex Acts, Soul Sex, Telepathic Underwater Jell-O Knotting Orgy, Threesome, Waterfall’s Hot Dog Orgy Block Party, What Can I Say Except You’re Welcome, Worldbuilding, Xenophilia, advanced monsterfucking techniques for thoughtful adults, and i've never been more proud, and various nonhuman genitalia, continuum mechanics, moresome, now with exposition, quantum physics, response so far indicates this is even weirder than the tags suggest, starring Sans
Language: English
Status: Completed
Published: 2019-08-12
Updated: 2019-08-12
Packaged: 2020-08-19 23:44:22
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 8,070
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20218252
Author URL: https://archiveofourown.org/users/Gilded_Pleasure/pseuds/Gilded_Pleasure
Summary: When Sans has a load of laundry he’d rather his brother didn’t touch, he takes it over to Waterfall and sticks it under a rock for the river to clean. One lucky Laundry Day finds him in the crosshairs of a very sexy opportunity all monsters have heard of, but very few have actually been offered.Just because he’s never actually done this before, that’s no reason to lose his chill...right?***It was requested Unto Me that I rewrite Laundry Day as a mostly spoiler free oneshot with some extra exposition about my continuum mechanics-based alternate-physics magic system, and I must accept for secret reasons.Consider this a kinder, gentler homage to my OG monsterfucker inspirat0rsOctavia Butler: unparalleled innovator of eldritch horror + existential reproductive angst&James Tiptree Jr: unexpected woman, vore-acious hard SF pioneer, and murderer





	Laundry Day

Sans is putting the last rock on top of his grungiest spare hoodie when he feels the inquiring spore land lightly on the tip of one of his vertebral processes, exposed by the downward bend of his neck. He gasps and shivers all over, sockets going perfectly round.

Oh...wow.

He wasn’t expecting _this_, but no one ever does, do they.

Here he is in Waterfall, just another boring old Laundry Day, and he might be about to be presented with an opportunity most monsters have heard of, but few have actually...experienced.

_Oh My_, the rock comments dryly. _You had better finish up, then._

“yeah,” Sans breathes softly, winks and gives a few coins to the rock to hold down his laundry until the current washes it clean. He’ll probably get it back once he comes to collect it; rocks tend to be pretty solid dudes. Heh.

He shivers lightly, then turns around to face the Moldbygg curious as to whether or not Sans is DTF.

Sans is interested in figuring out if Sans is DTF, too.

He heaves around to face away from the riverbank, groans his dumpy body into a cross-legged sitting position and waits with an anticipatory grin. He leans back on his hands so he can look up and watch the sexy wiggle, too. That’s part of it; he knows at least that much. He’s seen this happen before, just never to him. In fact, after a little bit he notices Woshua and Temmie have come to witness. Understandable. He feels extra special now.

Another spore touches him after a little while.

Is Sans interested in intimacy?

“yeah,” he replies quietly, smiling up at the gelatinous monster giving him a sexy pop quiz.

Will Sans taste and be tasted?

He nods, pleased.

Will Sans see and be seen?

“heh…yeah.” His sockets go flat on the bottom; he feels...peaceful. This _is _nice.

Will Sans touch and be touched?

“yeah,” he whispers, leaning forward and unconsciously stroking a finger along his ankle, slipping smooth, sensitive bone under the sock covering it.

Will Sans give and receive pushed magic?

“no,” he answers gently, face soft and relaxed.

Moldbygg notices Sans is permeable. Will Sans hold and be held?

Sans feels his breathing quicken. “_yeah_,” he whispers emphatically. Then he shivers all over as fragrant spores patter down on him, seeking the permeable magic between his bones to whisper endearments, enticements, and a few rather frank suggestions. Sans giggles, and lurches up awkwardly to his slippered feet.

Moldbygg wiggles off, and Sans shuffles along in its wake. Temmie and Woshua trundle along idly behind, chatting and sending messages. Sans doesn’t usually walk this much if he can help it, but it’d be rude to skip this part of the festivities under the circumstances.

As they approach the grotto he sees a few people set up sheetmetal grills a lot like his up top, and to either side of one of the waterfalls that gives this region its name. Roasting ‘cats and ‘dogs can take a while. Moldbygg must have been on the hunt for quite some time, since people are already eating. Sans spares a return wink for Aaron as he presses two ‘dogs into his hand; he doesn’t begrudge Aaron’s pushiness today, since it’s a special occasion. He can already tell by the smell and appearance that they’re not as good as Sans makes himself, but he’ll still eat them once he has a chance to sit and relax a bit. It’s nothing a lot of ketchup can’t fix.

They get behind the waterfall and Sans takes a subtle look around. His tight grin relaxes a bit; he’s had worse audiences.

“heya,” he greets idly as he shuffles toward Undyne, who still has most of her armor on.

“SANS?!! Hah...didn’t realize you were into this sort of thing?? Guess I’m not _that _surprised, but...”

Sans just shrugs mysteriously as he approaches the wall next to her, then slides down onto his shorts-clad skeleton butt and hands her one of his ‘dogs. She makes it disappear in two toothy bites.

He’s glad enough to see her, since that’s one less message he’ll have to send. Speaking of which. He sets his own ‘dog on his knee, rummages for a few minutes at the phone in his pocket, then sighs and starts tearing his food up to shove into the narrow gap between his teeth. His mandible is fused to the fossa on the right side, which often makes eating into a chore. He keeps at it with more follow through than he can usually muster up, since he’ll probably need the energy even if he’s not sharing. Takes magic to _make_ magic, after all.

Heh.

“Come here often?” he asks with a wink after his food’s gone, along with a bottle of ketchup to add some flavor to Aaron’s bland cooking. He glances up and over at Undyne’s bemused and singular eyeroll as Moldbygg continues to arrive, along with...huh, Loren’s here too? Nice. “you need help out with that?”

Undyne’s got her arms twisted up wrestling with one of the straps of her breastplate; she rolls her eye again and turns around demandingly after a few more minutes of hollering, cursing, and grunting. With the help of Sans’s nimble phalanges, Undyne’s in the buff in less time than it took him to eat. She glances over, elbows balanced on her lean, scaly legs and raises her eyebrow. She’s still got her eyepatch on; Sans can appreciate the dedication to accessorizing.

“Do _you_ need help?” she snickers wickedly; Sans feels his magic seethe in his face as he looks around at the other boss monsters scattered here and there around the periphery chatting, eating, or just chilling peacefully. Oh. Nice Cream Guy’s here too, cart and all, his blue-furred cunny already flapping in the nonexistent breeze; Dogaressa’s armor is in a neat pile of its own with her battle axe crowning it like a cake topper, and Loren doesn’t wear clothes anyhow. Oh.

…Sans is the only one still dressed.

He shrugs again, doffs hoodie and shirt, doesn’t even need to stand to slide his shorts down and off. He pats his discarded garments into a lopsided pile and sits on it, nice and comfy. He’s still got his socks and slippers on, gives Undyne and her eyepatch a wink. Neither he nor Undyne have any genitalia; no surprises there since monsters who _do_ have a slightly different scent than those who don’t. Sans’s gaze is drawn back to Blu’s cart. Come to think of it…

He rummages under his buttbones into the pocket of his hoodie, then looks for something in his phone. Pulls out a fistful of G and lurches to his slippered feet with a groan and a lazy grin.

“Hey!!” He pauses, looks at Undyne. They’re almost eye level with him standing, and she hands him a few more coins. “Get me something, too! Gotta give it my ALL, right?”

“…what kind?”

Undyne grins sharply, but just shrugs. “Whatever looks good!_ Surprise_ me!!” He takes the coins, but hesitates and looks down into the G in his compressed metacarpals thoughtfully.

“thought you had real specific tastes?” he questions lightly, and Undyne blushes a furious greenish pink in his peripheral primary vision. Sans’s magic surges over his skull too; that’s pretty nosy, even for him.

She shrugs, averts her eye. “It’s a special occasion,” she tells the wall sincerely, so Sans just nods and shuffles off feeling mildly chastened. You certainly couldn’t tell to look at him, though, and that’s comforting at least. Undyne didn’t _have_ to answer, but she had in her own way anyhow. Maybe his tells are a little more obvious than he’d like to believe.

Sans _doesn’t_ actually do this sort of thing much. Or…ever.

He’s nervous.

He shoots the shit with Blu at his cart for a little bit, haggling the price to something reasonable. From this angle he can see Punk Hamster and Fawn murmuring to each other snarkily. They’re probably trying to come off as aloof and cynical, but they mostly just look like they wish they were still wearing clothes. Honestly, the only person here Sans would usually be remotely interested in is probably Blu, who gets around almost as much as Sans does. He gives him his best grin and has it returned sincerely enough to make magic seethe across his skull lightly. The appetizing, familiar, and alluring fragrance of rabbit monster puts him at ease.

Dogaressa comes over for some nice cream while Sans is laboriously eating and gossiping amiably, and Sans discovers that he’s finding her surprisingly appealing too. Her marriage collar jangles comfortingly as she haggles with Blu. The scent of Dogaressa’s genitalia's not as strong as Blu’s since she’s not aroused yet, but between the two of them he starts to feel almost at home. He lingers to purchase and consume another nice cream and tell a few bad jokes; the compliments are heartening and Dogaressa’s less mean without Dogamy to look tough in front of.

He can tell they both like that he’s naked too; monsters with genitalia usually cover it, and theirs is exposed except for downy screens of delicate fur. Although San’s pelvis is just bones held together with magic, he and his brother always wear clothing in the style of monsters from Snowdin who do have something to cover, so his nudity feels a little more loaded than Loren’s or Undyne’s. It seems like he’s helping Blu an Dogaressa feel more comfortable as well, and it relaxes him further to know they’re all maybe a little nervous.

He returns to Undyne about 50 G lighter and two nice creams fatter, then hands her the pink one he’d gotten free under the pretext of the aforementioned special occasion.

Undyne’s licking her fingers idly when her yellow gaze goes hooded and soft.

Sans follows it, and it looks like...oh. Moldbygg’s more than doubled in size, and still arriving. Filling up a pretty big space in the center of the grotto, too; no wonder everyone’s sitting around the walls.

“so, uh.” Sans hears himself make a dry little noise in his skull as he watches Moldbygg join itself some more. Strokes his crossed ankles with his thumbs under the socks. “what happens from here?”

Undyne’s expression is still soft, her posture uncharacteristically relaxed in the periphery of the primary dimension of his vision. Bold and righteous in his secondary vision, exactly where she wants to be in his tertiary.

“Just go in whenever you’re ready,” she says, voice soft and dreamlike. The anticipation in it makes Sans blush again; wow. This really has him jumping out of his bones, doesn’t it? Maybe he should just-

“If you don’t ever feel ready, you can stay right here,” she continues soft and steady, “or you can go out and enjoy yourself with everyone else, have something to eat. Find another partner, if you still feel like it.” Undyne’s smoldering gaze doesn’t waver from the blob in the center of the room.

“Smell ya later,” she says as she stands, then walks right into the wiggling mass in the center of the grotto and just sort of….gets absorbed.

A minute later, her eyepatch is expelled and lands neatly folded on top of her stacked armor.

Sans exhales in amusement, feels a deep shiver of something else and watches as one by one, the boss monster participants decide to leave or join according to their inclinations. Anyone can change their mind at any point of course, but only one person leaves. The rest eventually walk into the quivering orgy happening in the center of the cave.

Sans still isn’t sure. He stands and approaches, gazes into Moldbygg’s undulating body, the interior of which he can’t clearly perceive other than knowing everyone who went in is still in there. It’s exciting...and daunting.

A complex, snowflake-like spore descends very, very slowly. Sans could dodge it no matter what, but he appreciates the delicate approach nevertheless.

He holds out his hand, spreads his metacarpals and lets the spore kiss the permeable integral magic between them lightly.

Sans is invited and welcome; Sans is not required. Sans is desired; he will remain so if he decides to join those above, and his absence will not be grudged. He should know that if he decides to enter, he will not feel the kind of inhibitions he might be used to.

What Moldbygg does lies outside the usual boundaries. Although no one will be asked to do anything they don’t want, they will feel no qualms about asking for and offering anything they _do_.

Sans may touch, and speak.

He reaches out and spreads his fingers into the quivering, permeable body of Moldbygg. It does this with boss monsters because it enjoys their pleasure, enjoys their individuality, enjoys sharing itself and its peculiarities. The extra magic helps it reproduce, even though the boss monsters’ magic won’t be used in the usual way and none are obligated to provide theirs. What its body does when this happens allows for more instances when it’s done, although the amount and size may vary. That doesn’t really matter of course, since it’s all Moldbygg.

Sans notices his phalanges are exploring his own sternum curiously, and he frowns a moment. He’s getting over his shyness more quickly than he anticipated. Or maybe…

“you, uh. already doing that thing you said?” he asks Moldbygg quietly.

No. That only happens if Sans enters, although it knows the fragrance of its spores is very enticing. That’s why it asked him to touch instead of enter; it doesn’t want to sway him either way. This is Sans’s choice, and his desire remains his own.

Sans makes a gesture every monster can understand, no matter how they’re put together. He wants to expose his soul.

“mind if i take a minute?”

Moldbygg approves; it won’t look. When it’s all together like this, its control and attention is unparalleled. That’s why it can do what it does.

Sans smiles, takes his hand back and sits right where he is, bare bones clacking softly on the cool stone floor. The soles of his slippers meet as he leans a hand on them casually. His phalanges make soft rasps on his ribs and sternum as his expression grows vague and introspective. He lets out a soft breath as his soul condenses, and he exposes it with a remarkably similar gesture to the one he’d made to describe what he’s doing, fingers steepling before drawing away from his body as a delicately iridescent, inverted white heart-shape follows them.

He looks into himself for a long, fascinated moment.

There’s a few surprises in here, so he slides a phalanx right in and exhales in mellow satisfaction at his own expert touch. Cyan and yellow coalesce and swirl in to follow the shallow, curious slide of his fingertip; his breath trembles out slow with the pleasure of it. Touching his exposed soul with his body always fills him with a sharp-sweet sense of completion, an echoing resonance that aligns and balances him. This synchronizes his intent and emotions with what he wants to feel, inspires and generates desire, suggests things he might want to happen. It also just plain feels good.

Touching yourself in front of someone is a deeply sexual act, even if they aren’t necessarily looking. His breathing deepens as his sockets drift half-mast, and he feels the points of his eyes expanding inside them loosely, changing texture with patient yearning.

Sans isn’t exactly the most sexually experienced monster in the underground. He’d spent the majority of his adulthood vaguely uninterested in showing his soul to anyone else, when he’d bothered to think about it at all...up until relatively recently. Not that he doesn’t have a perfectly natural and frequently nurtured relationship with _himself_, of course. Especially when he’s had trouble sleeping, has a bad day and doesn’t feel like company, or when he has a good day and it occurs to him it could possibly get even _better_.

Not that he was some kind of an innocent or anything, but the proposal currently on the table is a lot more intimate than slacking off and smoking treats with Doggo, then wandering out in the woods behind his sentry station for hugs and handjobs. That had been a lot of fun while it lasted; he’d liked the happy little yelps he made, the whispered encouragement, and the hot tongue licking his vertebrae. And considering Sans doesn’t have anything except bones for anyone to lick, that’s all they’d ever really got up to (well, except for _that one time_; Sans had liked that too but he blushes just thinking about it, so he doesn’t if he can help it).

Doggo bragging to the Dog Squad at Grillby’s about the sexy tricks Sans’s hands could do he’d liked quite a bit _less_. Not like he was _mad_ or anything, but he coincidentally stopped going by Doggo’s station after that. That had been a long time ago, too long to really tell _how_ long. That’s the way things are down here: a week could be twice that; an hour can feel like a month. But every once in a while Sans still manages to find time (heh) to set up a few pinecones above Doggo’s station, then takes a shortcut to stand perfectly motionless nearby when the wind pushes them off onto the roof, grin smug and sockets narrowed as he watches him yapping furiously at nothing at all.

No one takes what Doggo says quite as seriously as they used to.

There’s a certain justice to that, isn’t there.

It had occurred to him very belatedly and for no particular reason that he _might_ be interested in sharing his soul with someone else after all, and after a great deal of speculation, conversation, and fantasizing, he and Grillby had discovered they were remarkably compatible in certain ways. Grillby’s body is so hot and volatile, not only can Sans taste his shed magic (and get little glimpses of emotion and communication along with it) right on his bones, the spaces between Sans’s bones are still part of his body. The magic that holds them together is just _permeable_: physical substance can go right through it, and other types of permeable magic can interact with it in some interesting ways.

Grillby’s ceaselessly combusting integral magic is as permeable or as solid as Grillby wants it to be, and that has some extremely gratifying results when they spend time together in Grillby’s fireproof bed in his room above the bar. Although Sans has shared his soul with a few other monsters, Grillby’s the only one he does so with on a regular basis.

And it’s nice. He certainly enjoys himself, and he knows without doubt Grillby does as well. Monsters can give and receive a lot of pleasure just from looking at each others’ exposed souls, and feel even more by touching them with their bodies. Sans (also known to some as ‘Handsy Sansy’ thanks to Doggo’s fat yap), of course, uses his _hands_ for that sort of thing.

He hears his breath get a little faster as he spreads his fingers into himself, draws them down and nudges his thumb into the little cleft underneath.

What monsters like is different. Their bodies are different, and some don’t do certain things at all. Sans still has plenty he doesn’t do, and he’s certainly not unique in that. Like merging souls together with another monster. Most don’t do that just for pleasure since it requires a great deal of trust and caution, and also because that’s the first half of how you end up increasing the monster population.

The second half is also something Sans doesn’t do, although unless you’re _merged_ first there’s no chance of getting carried away and having a kid you didn’t intend to. All monsters shed magic in some form when they get just about any kind of worked up or agitated, and that includes sexual arousal; tasting and being tasted that way is a sexual experience on its own. For most of them it’s a kind of liquid, for others it can be spores, fragrance, or sparks and smoke in Grillby’s case. Even more intense is when a monster _pushes_ out their magic with the strength of sexual intent, especially and specifically into another monster’s soul while they touch it. Done alone, it’s an intensely gratifying experience to share with someone; if magic is pushed inside while souls are merged it can catalyze the germination of an additional soul in one or both.

Regardless, Sans doesn’t let other monsters push their magic into his soul at all, and he doesn’t push his into theirs. He only does himself, and if he’s honest he has a very hard time believing anyone else’s magic could feel even half as good as his own does. He and Grillby like to touch each other while pushing their own magic into their own souls almost every time they go somewhere private together. Sans doesn’t feel like he’s missing out on a damn thing…it’s so intense, he gets antsy just thinking about it.

He has a lot of reason to believe that what Moldbygg’s considering offering him is… not more, but something very different. It doesn’t reproduce in the way boss monsters do, after all. Doesn’t ‘have kids’ or anything like that. It just _increases_, and it likes to proposition boss monsters to help when it gets in an expansive mood.

It’s Sans’s understanding that Moldbygg can form connections between the monsters it invites into its body that are less intimate and more flexible than what most boss monsters usually experience. Monsters don’t have stigma surrounding soul based acts of sexuality, but excessive physical touching is considered to be somewhat prurient, and focusing on genitalia for monsters who have it is considered a slightly immature form of sexuality, especially if souls aren’t involved. Far more people know what he does with Grillby than what he got up to with Doggo, but only the latter is gossip-worthy.

The reason people know what he gets up to with Grillby is of course the same reason there’s a bunch of people roasting ‘dogs and ‘cats around and on top of the grotto he’s in right now: monsters all share a vague awareness when someone’s soul is condensed and exposed nearby. Being able to sense it isn’t a sex thing, regardless of the reason the soul’s exposed. It’s not like seeing or overhearing (not that the latter’s even something worth acknowledging). It’s just an atmosphere of calm and safety, because only safe, calm monsters expose their souls with themselves or a partner. The emotions and ambience generated by this many exposed souls at once, combined with what Moldbygg’s doing, well.

Sans has been one of the celebrants outside the grotto before.

When he imagines feeling “the sun” on his bones, it’s the same sort of feeling. Warmth, compassion, life, hope, love and healing, more than enough for everyone.

That’s something he’d love to provide, something he’s interested in sharing with everyone.

Sans spreads his fingers and pushes them deep into himself, finds a few more points of interest and desire that make him smile. Then he reaches out and touches the quivering change in atmosphere that demarcates the beginning of Moldbygg’s body. He’s interested, and he wants to know more. Moldbygg quivers with delight, lets its spores seek permeable magic between metacarpals again.

Pleasurable acts will be performed and received by the boss monster participants, but _responsibility_ for them is passed to Moldbygg whereupon they are absorbed and processed into...huh. It matters less _what_ he wants than that he does want it, because Moldbygg’s desire is to experience desire and enjoy its fulfillment. This circumstance allows for a degree of permissiveness the participants can also enjoy along with it.

Sans has been invited to experience intimacy with Moldbygg. That is what will happen; the _vehicle _of that experience is the other participants. Sans will also be the vehicle, delivering pleasure to them in turn. In certain cases, Moldbygg’s body may also be involved to add to the enjoyment of monsters whose own bodies or inclinations might not otherwise be compatible.

That’s something they’ve all heard about, one of the ways this experience is considered truly unique.

Sans shivers deep; Moldbygg _likes_ that Sans wants much more explanation than most, wants to understand it in a way few of its partners ask for. Again, all it wants is that Sans experiences desire and its fulfillment; _what_ he wants and gets is secondary. An explanation is an unexpected novelty, and Sans is already doing what Moldbygg likes.

Enough that it would seem that Sans is pushing his magic into himself in response with a soft, emphatic exhale; his upper body leans out over his legs as he trembles under the flood of his own sweet peace. This is more than touching, this is putting his body inside his soul physically, where it will stay until it’s absorbed. His magic will hold the shape of the intent it was pushed with, letting him feel emotions and sensations he wants to linger. The slow absorption can take a few hours or a few days, depending on how much he puts in there.

It not only feels good when it goes inside, it feels good to push it out: a spreading, quivery-full warmth that gives rise to an even more intense sensation of _completion_. It’s so good he just keeps on going, glad he had the second nice cream after all. He faintly hears his own quiet, satisfied moan as he encourages his magic to become not-part of him right where he touches himself, fingers sinking in deep to make this calm-complete feeling stay inside him for as long as he decides to do whatever this ends up being.

Moldbygg quivers around his fingerbones. Once again Sans delivers exactly what it wants: the physical contact helps it experience his desire and its fulfillment. He puts himself back, and once he’s done shivering through the rush of his magic-soaked soul joining back into itself, the gelatinous magic of its body firms up around his hand to help him lurch to his feet.

With a dreamy grin, Sans goes inside.

It’s like being underwater without actually being underwater. Sans can tell he weighs less, yet there’s more drag on his limbs as he moves. He hears something, but it’s not sound; the inside of Moldbygg’s body can’t carry that kind of subtle, complex vibration. Moldbygg wants him to come out...in a different way than usual. Sans sits again and relaxes for a moment, shuts his sockets and lets its call brush through him gently.

Sans shivers as he feels the gelatinous monster’s desire for him call his soul forth once again, but it’s so subtle. So much gentler than when Grillby does it. The fire elemental’s call is hot and rough, impatient and needy just like his soul, and Sans loves it. This, though...this is already so different. He exhales and feels his eyes relax too; he feels the deep, delicious tug of his soul being pulled but it’s….it’s softer even than his own call, it’s _good_. And then...oh, wow. It just _stays_ that way, a constant trembling thread of desire-fulfillment that mingles with his own, stable while still yearning. Still _pulling_ gentle and insistent, like it won’t ever end.

Sans looks down and sees a blurry outline of his soul inside his ribcage.

Moldbygg lets him know this is how he will feel and know/be known. This is a bit like the sensation caused by the spores, but it’s all over now, it’s...consistent. Arousing, soothing, and surprisingly informative. Makes him curious, makes him wonder what will happen next.

Sans feels his own smile echoed back into his soul as his sockets narrow; he feels eager to please.

Nice.

Turns out Blu wants his cunny touched, and Sans _really_ wants to touch it. Something familiar, something he knows he likes (something he’s good at; his desire to please grows keen). They find their way into each other’s arms easily, kneel down facing each other since it’s easy to keep balanced in this lightweight, dim interior. He notices that Blu has a dim outline of an inverted heart on his belly; it’s condensed without being fully exposed, so he’s also touching himself in a way that leaves his hands free. It makes Sans smile; monsters with hands usually prefer to use them for touching, but he can see how in this particular configuration that might be cumbersome.

Sans pets the soft, furry little triangle between Blu’s legs for a long time, holds him close and strokes his back encouragingly with the distal phalanges of his other hand. He tilts his skull back to have his face nuzzled as he finally presses with his wrist, slips his smooth fingertips inside the exposed bud of his genitalia. He feels Blu’s arms shiver around him. Sans curves his phalanges in tight at the front wall, beckons gently there until he feels the sweet spot inside firm right up.

Blu can sense the care and expertise in his bone fingers. It’s been so long since he’s been touched here, and he...he’s never been touched like _this_. Rabbits usually use one finger since their genitalia's small for their body size, but Sans’s fingers are so narrow and delicate, he can use two or...yes, that’s a third. The nubbly-smooth texture of his phalanges is an added layer of novel sensation, and he can also feel how much Sans likes to do this. No hesitation from Sans, no anxiety. Just the confident slide of magic-damped bones curling in and teasing, spreading to open and fill him.

Blu really likes how much Sans wants to be held and pet too, pulls him close and tight while he pleasures him, nuzzling and cuddling magic-sheered bone.

Sans’s voice makes a sound that doesn’t carry when a dry little rabbit tongue flicks out to taste; it doesn’t need to since Moldbygg’s taking care of that, but he wants to give Sans the physical sensation that usually goes along with being tasted anyways. Sans smiles warmly, rubs his face along Blu’s cheek and neck to savor how soft and sweet-smelling his fur is. Warmth and spice, something even more compelling and addictively pleasant underneath.

He feels Blu’s pleased grin bloom; it’s the scent of his magic Sans is enjoying. Shed for and with pleasure, close to his skin under the fur to help enhance desire for whatever he already wanted. This fragrance stays close and doesn’t carry; only his partners will enjoy what amounts to an aphrodisiac under the circumstances. Makes Sans want even more touching, makes him want to feel like this too, wants to be touched…_inside_. Blu’s using his hand in Sans’s pelvis now; the soft-furred palm that slides firm along the inner curve of his sacrum has him shuddering hard in no time flat. Doesn’t feel like being touched by fire, softer than claws… Blu’s touch fumbles a little, slowing to fits and starts as he squeezes Sans rhythmically with his other arm.

A soft wave of apology from Blu; he’s working up to something, and Moldbygg lets Sans know he’ll get his turn too if he wants, but… it seems Sans is too good at this for Blu to concentrate right now.

Sans feels joy bloom in his soul and leans Blu back, gratified and flattered by that more deeply than he’d usually be willing to admit, even to himself. He giggles a bit when he feels the light tinge of emotional backwash as everyone in here with him also enjoys his gratification, although they might not necessarily know its source. Then Sans stops thinking so much and just gives in to feeling: the hot, soft little cunny quivering up tight around his ceaselessly working fingers, the furry arms around him petting and squeezing the patterns of his pleasure into his bones, the soundless impression of happy cries of pleasure and satisfaction as Blu shivers himself to completion in Sans’s bony palm.

Blu’s still fine with touching Sans, but he doesn’t want to as much as two others want something Moldbygg knows Sans is willing to give them. What Blu really wants most after his climax is for everyone to enjoy how nice he smells, and Dogaressa and Undyne approach since they certainly want both Blu’s fragrance along with the various tactile pleasures it turns out Sans is willing to provide them.

Dogaressa kneels behind him, her big hands stroking his bones until he shivers and tries to moan, voice disassembling itself out into Moldbygg’s body to be processed into pleasurable spores for everyone to taste if they like. He leans back into her strength, letting her enjoy his unusual smooth-hard body, the pads of her broad fingers tasting and testing its frail brittleness, playing and pushing at the soft, intriguing resistance between his bones.

Undyne kneels in front of him, straddling the lazy fur-lump of Blu, who’s just as glad to lie there motionless and be appreciated. Sans smiles; he can relate. Undyne wants her hair played with, because it’s not actually hair in the same way furry or hairy monsters have. It’s thin tendrils of sensitive fins, and Sans’s phalanges are perfectly shaped to card through it again and again.

It makes her feel pretty and soft; she keeps it bound most of the time for a reason. When she lets it flow free, a wave of quintessentially _feminine_ sensuality washes through everyone. Even Loren, who doesn’t actually want any sex, just the somersaults they’ve been weightlessly performing somewhere above them all for the duration. Loren quivers with harmless, delicious transgression as they enjoy the vicarious thrill of _gender_, a decadence they usually wouldn’t indulge in.

Punk Hamster and Fawn are in here somewhere too, souls already merged together and pushing their magic into each other with gusto as they pet, taste, and spend to heighten the sensations even further. Apparently they plan to take full advantage of the contraceptive effects of being inside Moldbygg’s body: the only result of any and all acts for the duration will be more instances of Moldbygg. That’s what they’re here for; their desire is to perform reproductive acts without reproductive results. Their feelings of abandon and indulgence spice the already permissive atmosphere with a compellingly carnal energy to balance out the intensity of Loren’s self-sustaining cycle of nonsexual desire and gratification.

Everyone quivers along with them, and the effect on Sans directs his desire towards something his body lets Moldbygg know is… complicated. What Sans wants and what his body will permit has a few gaps it leaves unbridged for good reason. Well. Moldbygg feels more than up to a challenge, especially when the rewards so far have been downright gratuitous.

Moldbygg does something that causes its body to solidify only in the space it occupies inside Sans’s pelvis, and he gasps in some of its gelatinous substance through his nasal cavity when it also gets _hot_. Its body can blend with his in a way that isn’t possible for nonpermeable bodies; it feels a little like when Grillby goes in there but softer, gentler than the almost-dangerous, thrilling touch of fire. Dogaressa explores the magic in Sans’s pelvis cautiously with her fingers as he leans gratefully into her touch, probes until she finds a spot where he can be penetrated.

Sans shudders hard as her fingers open him, gasping in even more of Moldbygg’s body as the sensation of fullness and movement travels through his newly dense magic to transfer the deep caress to the insides of his pelvic bones. He likes the blunt play of her fingers, loves the sheer physicality of the pleasure happening in his body. It’s like the best parts of stuffing his soft blanket in his pelvis on his own, and the times he’s been touched in there by partners mashed up together into something so exquisite he thinks he can’t possibly hold more sensation.

Then Dogaressa pushes her thick cock inside him from behind, and the impression of Sans’s beautiful, carefree laugh rings through everyone like a wide golden bell as he realizes just how much intensity he can take.

A wave of heat, fullness, and pressure slides deep into his body, then retreats to let it flutter closed behind the delicious intrusion.

Sans wraps his arms up loosely around Undyne’s shoulders, swooning with the overwhelming sensations happening inside his pelvis. She hugs him tight and supportive; he actually kind of needs the help at this point to stay upright, and he shakes hard when she caresses his parietal bone firm-smooth just how he likes. He tucks his face into her neck gently with a heavy not-sigh. There’s not actually any air in here, but the interior is perfectly breathable for all involved.

Blu takes over petting Undyne’s hair, because Sans is...yeah, all his attention’s been stolen by the push and pull in his pelvis, the gentle hands exploring his ilium as he’s meticulously, considerately fucked. Sans’s laugh rings silent-sweet through all of them again; he thinks very privately that this is _way_ better than when Doggo tried to do something like it.

Sans can feel how he and Dogaressa are actually sharing _Moldbygg’s_ body; it’s blended into the permeable magic in his pelvis, thickening it into something that can pleasure them both. Their blended magic tightens around her hot and trembling, giving her a soft opening filled with just-Sans to slide her genitalia through as her blunt, strong fingers find a reverent grip on Sans’s iliac crests. The delicious shaking of his bones shimmies through it to stimulate and encourage her thrusting, and a hint of her taste travels through it to enhance Sans’s feelings of satisfied repletion. Sans parts his hidden teeth the tiniest amount near Undyne’s smooth-scaled, featureless chest, and a spore materializes eagerly to drift slowly into his mouth.

Sans’s arousal is so strong, his _soul’s _so strong everyone shivers with it in unison.

Dogaressa’s inherent femininity resonates deeply with Undyne. They lean in towards each other over Sans’s shoulder to practice making out like in the anime Undyne watches with Alphys. Sharp teeth and soft tongues test each other eagerly, and Sans feels vaguely aware that Undyne’s pushing magic inside herself with the thrill of _kissing_. Dogaressa caresses bones encouragingly, moves in Sans faster because Undyne is so gentle and soft, so _beautiful_, she’s...she-

Dogaressa’s abrupt pseudoclimax swells her cock up so big Sans can practically taste it. Moldbygg pushes enough surprised fullness into Sans’s pelvis that the magic holding it together expands along with it, spreading the pubic symphysis and sacroiliac joints apart slightly.

The pleasurably violent shudder that tears through of all Sans’s bones at once is unexpectedly stimulating to the interior they’re playing in. A torrent of delight goes through Moldbygg, and the drenching sweetness of Sans’s spent magic dissolves out into everyone except Loren, who won’t taste or be tasted.

The resulting flash flood of sensation’s a bit much even for Undyne (especially with her hair out), so she gives Dogaressa a final peck, Sans an affectionate pat, and floats up to go have some somersaults with Loren for a little while. They’re very flattered by Undyne’s appreciation of their stamina, and the two decide to have a friendly little competition.

Sans has played around with enough Dogs to be unsurprised that Dogaressa is only getting started; as Undyne drifts away he falls forward right into Blu’s arms where he still reclines, extending his upper body into his eager, warm embrace. The supportive grip maintained on his pelvis to prevent pulling at her knot too early leaves him bent over, and the heated pressure and movement they’re sharing inside his body intensifies further. His shaking phalanges comb through Blu’s fur again, drift down as his desire is stoked by Sans’s taste, lush and unctuous with his unusually deep capacity for pleasure.

Sans lets his normally keen awareness of time slip away. He gives himself up to Dogaressa’s energetic enjoyment of his body, uses all his concentration to finger Blu’s cunny to his usual standards, sharing the taste and scent of their mingled magic flooding through in ripples, then waves. Moldbygg’s appreciation for their remarkable enthusiasm’s moving things along for it faster than it had anticipated, and it is not displeased by that whatsoever.

It does make its spores spawn a bit more thickly than usual, and Blu surges up in response until Sans is suspended upright between his partners. He almost manages to choke on the substance he’s breathing instead of air as both of them start to touch and stroke his bones gently all over. His skull falls back onto Dogaressa’s shoulder, eyes spreading out so wide they go nearly as transparent as the space inside Moldbygg’s body; he shuts his sockets since he can’t see anymore anyways. Soft-furred bodies sandwich his violently trembling bones until he’s pressed suspended between them. Feels like he’s being hugged all over, inside and out.

Blu’s hips jerk out the rhythm of his pleasure tight around Sans’s stiff-curled phalanges, and the gentle peaks of his climax wash through everyone once again. As his cunny’s emptied with a lingeringly fond, wet-boned caress he takes gentle hold of Sans’s femurs. He bends and lifts his legs until he’s holding him up, folding Sans in half as his bone arms slide up and back to go around Dogaressa’s neck gently.

Blu smiles wickedly, gives Sans’s face a sweet little nuzzle. He knows what he’s doing, apparently; Sans shudders violently in anticipation. Blu’s hands slide into the crooks of Sans’s knees, and he keeps lifting until Sans and Dogaressa both arch openmouthed at the increasing tension on her engorged, knobby length.

The sweet, relentless pull where she’s locked tight into Sans’s thickened integral magic is drawing at something so deep and primal in her, she can’t resist any longer. The pressure mounts, and she leans forward until her careful teeth close firm on Blu’s shoulder, sparing Sans’s delicate bones to his passing and mild disappointment. After all, no one in here wants to feel Sans’s pain, only the intensity of his pleasure, and Blu wants the bite much more than Sans does anyways.

Blu’s magic sheds so much that Sans tastes a strong memory-impression of the way a Dog’s genitalia can feel rubbed against Blu’s; he’s far too small inside to be penetrated the way Sans is right now, but he likes the slick friction on his cunny and the firm pressure of teeth on his shoulders and arms. His body’s nice and sturdy, and he can take some rough play anytime he wants to. He reaches out and holds them both tight, moving in closer to let Dogaressa get a better grip with her jaws.

Dogaressa shakes almost as hard as Sans for a moment, hold loosening briefly so she can thrust a few more times. Sans’s moan drifts out into Moldbygg, he honestly can’t wait. Dogaressa staggers on her knees as she pulls down hard with her hips, as if she’s trying vainly to pull herself out of his body as it grips her even tighter. Sans knows she’s not; the pulling’s what stimulates her true climax. Here it is, accompanied by a gush of magic so spiced with toothsome pleasure Sans’s neck cranes back as he screams silently, then his skull falls forward as he gives in utterly.

He nudges his frontal bone dazedly on Blu’s soft, fragrant fur as Dogaressa’s spent magic continues to pool in his pelvis, drawn out of her and held inside him by the walls of Moldbygg’s thickened magic. It’s mimicking the sensations she’d feel doing this to another Dog as it clenches Sans’s integral magic down tight to trap her genitalia inside his body. It’s giving Sans what it picks up of the sensations she recalls from having this done in turn to her, pouring it into his remarkable capacity for this kind of physical intensity despite his delicate body. The increased pressure pulls even more pleasure out of her in long, winding skeins that make her jaws clamp down on Blu until he wraps his arms around them both, squeezing hard and shivering with the sharp, exhilarating pleasure of it.

Sans’s sockets stream into the gelatinous ether as his phalanges scrabble desperately at warm fur, because he, he can’t… he _needs_…

…needs _something_…

Sans’s body and Moldbygg reach a soundless agreement; Sans goes limp as Dogaressa’s blunt, soft fingers tickle light and repetitive at the slightly loosened, quivering-hot juncture of his smooth, bare pubic bones.

She hugs Blu closer to help hold Sans in place, shuffling on her knees and yanking down hard with her hips to put even more pressure on her genitalia as she spends endless and rhythmic inside Sans’s stuffed-spread and practically creaking pelvis. She’s shaking all over, a silent, ecstatic growl reverberating through bone and fur alike as she rubs her fat fingertip ever-so-slightly _inside_ his pubic symphysis, the joint spread by the tension Blu keeps on his wide-apart femurs.

No one could ever complain about Moldbygg’s timing. Sans almost faints when a nameless tension in him uncoils all at once; he spends out in a searing-sweet flood to mingle with Dogaressa’s magic as she finally pulls out of him as sudden as a cork from a bottle. Moldbygg catalyzes their mingled pleasure along with Blu’s addictive fragrance into spores so exquisite, Blu and Dogaressa don’t even mind missing out on the pseudomerge and shared push Moldbygg can’t bring itself to put off any longer. They’re too busy petting and cuddling the dazed and shivering skeleton between them, who hadn’t intended on participating in that portion of the festivities anyways.

In fact, Undyne ends up rejoining them because she craves one last indulgence after her physical exertions with Loren: the nap Sans wants more than he thinks he’s ever wanted anything in his life. They all fall into a soft-and-scaly, comfortably bony pile, and before Moldbygg’s even finished completing the merge they’re all fast asleep.

Sans wakes up under Blu’s now-heavy arms holding his bones against the furry chest beneath him, and looks up to flicker his eyes sleepily at the instance of Moldbygg towering above their reclining forms.

“heya,” he grins up at it muzzily. “how’s tricks?”

After a minute or two, a spore is produced and slowly descends towards Sans. He has plenty of time to glance over at the patted-together pile of his garments close to the wall, noticing that his slippers are set carefully on top, the socks tucked into the toes just like Sans always puts them when he’s otherwise disposed.

It’s sweet.

Then he blinks and sneezes as the spore lands in his left socket.

This instance of Moldbygg lingered to thank Sans for his contributions, and make sure he’s feeling okay. See if he needs anything. The reorganization went swimmingly (Sans giggles softly), and Blu and Sans are the last participants to depart. Punk Hamster and Fawn alone provided so much magic in response to the overwhelming pleasure Sans and his partners supplied, Moldbygg nearly doubled.

Sans’s magic seethes in his skull; even after all that, he doesn’t actually feel all that hungry. But...he could probably go for another nice cream, if he’s honest.

“glad to help. And, um…” Sans looks up at Moldbygg’s sexy wiggle. “thanks?” Sans sighs, then shifts experimentally. His body feels like it normally does; he’s also clean and dry, which he didn’t expect after that degree of shenanigans. He is also very much restrained by the furry arms around him.

“uh. you awake, blu?”

Moldbygg’s starting to depart, Sans interrupts to request help waking the rabbit monster clutching Sans to his chest like a comfort item. Working together they manage to rouse him eventually.

Blu and Sans get dressed together shyly, and Sans flirtatiously insists on paying double for the nice cream.

“_see _ya around,” Sans winks outrageously, catching a faint whiff of a very promising fragrance as he departs to seek his laundry.

Sans might have lost track of time, but it’s probably clean by now.

**Author's Note:**

> I’m sure you have at least one VERY pressing question after reading something like that. No worries, I have an answer for you!! To disambiguate: The reason Sans didn’t give Undyne any change back is because she wasn’t paying for nice cream, she was paying Sans to acquire an item for her regardless of cost. Monster money doesn’t work the same. ;)


End file.
